Citing better Medicare prescription coverage and other changes in the new law, Senate Majority Leader Harry Reid and his top lieutenants say the overhaul "is too important to be treated as collateral damage in a partisan mission to repeal health care."

The letter says repeal would have "unintended consequences" for the part of the law that gradually closes the Medicare prescription drug coverage gap, as well as for other popular consumer benefits.

Also signing the letter are Sens. Dick Durbin of Illinois, Charles Schumer of New York and Patty Murray of Washington.

A copy of the letter was obtained by The Associated Press.

Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Republicans are taking control of the House for the first time since 2006, while in the Senate they’ve gained six seats and can block most Democratic initiatives. Here are some of the important committee chairmen and the pivotal GOP senators who will help determine the outcome of legislative struggles with the Democrats over the next two years.

Rep. Spencer Bachus, chair, House Financial Services Committee

Gary Cameron
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Reuters

A soft-spoken Alabaman, Bachus will have a crucial role in overseeing banking, consumer protection and securities trading. His domain will include the Federal Reserve, the World Bank and the International Monetary Fund, as well as troubled government-owned mortgage guarantors Fannie Mae and Freddie Mac. He doesn’t have the rhetorical flash and stinging wit of his Democratic counterpart, Rep. Barney Frank, with whom he has often jousted. Bachus drew fire when he told The Birmingham News on Dec. 9 that, “In Washington, the view is that the banks are to be regulated, and my view is that Washington and the regulators are there to serve the banks.” He later amended that comment, saying that regulators should not micromanage banks, but should set ground rules for how they operate. “Bachus' staff is going to be very busy getting him to retract statements in which he reveals what he really believes about a fundamental issue before the Committee,” Frank said.

Brown’s victory in the Jan. 19, 2010 special election to fill out the unexpired term of Sen. Edward Kennedy signaled that the tide was turning against President Barack Obama and his allies in Congress. No Republican had won a Senate election in Massachusetts since 1972, when Brown was only 13 years old. Brown must run for re-election in 2012 and as a Republican senator from one of the nation’s most Democratic states, he’s a sensitive political indicator. With his vote being closely watched on every major issue, Brown voted for the Obama administration’s arms control treaty with Russia and for repealing the military “don’t ask, don’t tell” policy for gay service members. But he voted against the DREAM Act to grant legal residency to children of illegal immigrants, calling it "backdoor amnesty."

Rep. Eric Cantor, House majority leader

Jonathan Ernst
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Reuters

Elected in 2000, Cantor has risen to become one of his party’s most visible spokesman and a principal tactician for House Republicans. He got started in politics as a teenager by serving as a driver for Rep. Thomas Bliley, R-Va. Cantor now holds the Richmond-based House seat that Bliley once held.

Rep. David Dreier, chair, House Rules Committee

Harry Hamburg
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ASSOCIATED PRESS

One of several Californians in leadership positions in the new Republican majority, Dreier will have the job of designing the rules for each piece of legislation that comes to the House, including how many amendments the minority party can offer to bills. First elected in 1980, Dreier served as Rules Committee chairman from 1998 to 2006, when the GOP was in the majority. If process controls legislative substance, then Dreier is the one who’ll control the process.

Rep. Darrell Issa, chair, House Oversight and Government Reform Committee

Tim Sloan
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AFP - Getty Images

The grandson of Lebanese immigrants, Issa was born and raised in Cleveland and made his money in the car alarm business. He helped underwrite the recall effort against California Democratic Gov. Gray Davis in 2003 and spent $11 million on an unsuccessful bid to be GOP Senate candidate against Sen. Barbara Boxer in 1998. The six-term California Republican has promised to investigate vigorously alleged abuses of power by Obama administration officials. "Our committee is the committee of stopping government from taking away your liberties” and “stopping government from exceeding its authority,” he said.

Sen. Jon Kyl, Senate minority whip

Michael Reynolds
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EPA

Serving his third term in the Senate, after four terms in the House, Kyl is the chief GOP vote counter, figuring out members’ sentiment on bills and nominations. He’s up for re-election in 2012. The son of a former House member from Iowa, Kyl led the opposition to the Obama administration’s arms control treaty with Russia. “What we ought to be doing is focusing on Iran and North Korea and other places where maybe there is proliferation going on, and a desire to develop nuclear weapons that could potentially attack the United States,” he said.

Rep. Kevin McCarthy, House majority whip

Chip Somodevilla
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Getty Images

First elected in 2006 from a safe Republican district which includes his hometown, Bakersfield, Calif., McCarthy has vaulted with impressive speed to the third-ranking position in GOP House leadership. He’ll be the first Republican from California to serve as majority whip. McCarthy learned politics from his former boss, Rep. Bill Thomas, whose seat he won when Thomas retired. McCarthy was Republican leader when he served in the California Assembly. According to the Los Angeles Times, McCarthy has “an encyclopedic knowledge about his House colleagues' idiosyncrasies and political needs” and “has pored over the profiles of lawmakers and their districts in the thick Almanac of American Politics on flights between California and Washington.”

A native of Janesville, Wisc., Budget Committee chairman Ryan has long been his party’s most articulate spokesman on spending. If Republicans really intend to cut spending, Ryan can tell them exactly where and how to do it. But Ryan’s plan for a voucher system to replace the open-ended Medicare entitlement makes some Republicans skittish. In the 2008 election, President Obama carried Ryan’s congressional district with 51 percent of the vote.

Sen. Olympia Snowe, R-Maine

Chip Somodevilla
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Getty Images

Snowe is one of the decisive senators in the center whose vote often tells if a bill or amendment will pass. She is up for re-election in 2012. Obama won her state in 2008 with 58 percent of the vote. She opposed the Obama administration by voting against the DREAM Act to grant legal residency to children of illegal immigrants. She voted for the administration’s arms control treaty with Russia and for repealing the military “don’t ask, don’t tell” policy for gay service members.

Rep. Kristi Noem, R-S.D.

Harry Hamburg
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AP

South Dakota cattle rancher and ex-state legislator Kristi Noem is one of two members of the class of 2010 who’ll be part of the House GOP leadership. She defeated Democrat Rep. Stephanie Herseth Sandlin, getting 48 percent of the vote in a three-way race. Delivering the weekly address for her party on Dec. 11, Noem twice used the word “humble,” calling herself "part of a new majority committed to being humble, more modest ... We are committed to making sure Washington humbles itself ...” Noem was a college student when her father was killed in an accident on the family farm. “I was 22-years old, we got hit pretty hard with estate taxes at that point in time, and I really started to recognize the impact that government and taxes had on small businesses and in an agricultural state like South Dakota,” she told an interviewer.